The present invention relates to hydraulic apparatus for driving an element such as a concrete-mixer by means of a semi-trailer motorizing system, alternately with the semi-trailer, which is coupled to a tractor for travel along the road and on-site work and which supports the concrete-mixer.
In addition, the invention also relates to hydraulic apparatus for driving an element constituted by a supplementary hydraulic circuit and adapted for controlling for example hydraulic rams, boring tools, winches or like apparatus, by means of a hydrostatic motorizing system employed when the vehicule is travelling and pulling the semi-trailer.
Some systems for motorizing the axles of semi-trailers comprise, on the semi-trailer, a hydraulic motor which may or may not be connected to a de-clutchable speed reducing transfer box normally intended to drive one or more drive axles of the semi-trailer.
An object of the invention is to use completely or partly this system for motorizing the semi-trailer for performing various functions which have normally been performed up to the present time by the engine of the tractor simultaneously or alternately with the use of the motorizing system.
French patent application No. 80 26 650 of Dec. 16, 1980 discloses a closed hydrostatic system for motorizing the semi-trailer, while French patent application No. 81 21 742 of Nov. 20, 1981 relates to a safety hydraulic circuit connected to the piping of the hydrostatic system for motorizing disclosed in the preceding application. The present invention provides special applications capable of being achieved with these devices in particular, but not exclusively, any other motorizing systems provided for a semi-trailer coupled to a tractor for movement along the road and for on site work could possibly be provided.
Further, the element adapted to being driven by the hydraulic apparatus of the invention may be a concrete mixer, for example disposed on the semi-trailer, but the concrete-mixer may be completed by any other element which is mounted on the semi-trailer and which is capable of being driven by the de-clutchable speed reducing gearbox of the motorizing system with which the semi-trailer is provided.
In this case, the element is a supplementary hydraulic circuit adapted for example to control one or more hydraulic rams, an unloading conveyor, or a concrete pump etc.
Concrete-mixers mounted on a semi-trailer or on the supporting vehicle itself are driven in rotation at the present time in two ways:
1. By a direct power take-off from the motor of the tractor connected to a hydrostatic circuit of closed type whereby it is possible to vary the direction and the speed of rotation of the tank of the concrete-mixer. The power required for rotating the latter is therefore taken from the engine of the vehicle. The variable-output hydraulic pump, the main component of the hydrostatic circuit, is provided with a regulating system known per se, permitting the obtainment of a relatively constant output or flow irrespective of the variations in the running speed of the engine of the vehicle in the course of its use on the road, and accelerations produced by the action of the driver on the accelerator. A manual control permits a multiplication of the value of the desired flow and the direction of the fluid for supplying the fluid to the hydraulic motor driving the drum of the concrete-mixer.
2. By an additional or auxiliary engine which is provided in addition to the engine of the vehicle and which replaces the latter for driving the concrete-mixer in its various functions. This auxiliary engine drives a variable-flow pump supplying fluid to the hydraulic motor which rotates the concrete mixer. A manual control permits varying the speed and the direction of rotation of the tank or drum of the concrete-mixer. This additional engine must, as in the preceding case, be of sufficient power to ensure the following functions related to the use of the concrete-mixer:
(a) Stirring or agitation of the concrete in a first direction of rotation at low speed (one to four rpm), the vehicle being in motion or stationery.
(b) Mixing in a first direction of rotation at low or high speed (1 to 8 rpm), the vehicle being stationery.
(c) Emptying in the second direction of rotation of the concrete mixer at high speed (1 to 16 rpm), the vehicle being stationery.
(d) Cleaning in one or the other of the two directions of rotation at high speed (1 to 20 rpm), the vehicle being stationery.
The drawbacks of these two types of devices are the following:
The driving of the concrete-mixer while the vehicle is travelling is effected to the detriment of the power of the engine for use on the road, the rotation of the tank is not really at constant speed owing to the response time of the regulating circuit, and the consumption of fuel on the part of the tractor vehicle is substantially increased.
A direct drive from the engine of the tractor must also be made available, which is rarely provided for by manufacturers and consequently limits the development of this system, the motorizing means being preferably mounted on the two take-off connections of the gearbox, provided the ratio of the speed with the engine is constant. Lastly, in the case of an accidental stoppage of the engine of the tractor, for example on the occasion of an accident on the road, the rotation of the concrete-mixer stops, the concrete sets in the mixer and the concrete-mixer is lost.
The drawback of the second known type of construction, i.e. an auxiliary engine driving a pump supplying fluid to a hydraulic motor coupled to the concrete-mixer, resides essentially in the weight and the high cost of this equipment due to the necessity to have available sufficient power for driving the concrete mixer up to 20 rpm. Consequently, at the present time, power of the order of 100 H.P. for this auxiliary engine is required.